Radiation image acquisition device

ABSTRACT

A radiation image acquisition device includes: a radiation source which emits radiation; a wavelength conversion member which generates scintillation light according to incidence of the radiation emitted from the radiation source and transmitted by an object; first imaging means which condenses and images the scintillation light emitted from an entrance surface for the radiation in the wavelength conversion member; and second imaging means which condenses and images the scintillation light emitted from a surface opposite to the entrance surface in the wavelength conversion member, wherein one of the first imaging means and the second imaging means condenses the scintillation light emitted from the entrance surface or the opposite surface in a direction of a normal thereto, and wherein the other condenses the scintillation light emitted from the entrance surface or the opposite surface in a direction inclined with respect to a direction of a normal thereto.

This is a continuation application of copending application Ser. No. 13/981,372 filed on Oct. 1, 2013, which is a national stage application of PCT Application No. PCT/JP2011/074330 filed on Oct. 21, 2011, designating the U.S.A.; the entire contents of each of these are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a radiation image acquisition device.

BACKGROUND ART

There is the conventionally known apparatus for applying X-rays emitted from an X-ray source and transmitted by an imaging object, onto a scintillator of a flat plate shape, detecting visible light (scintillation light) generated in the scintillator, by solid-state photodetectors laid on both surfaces of the scintillator, and superimposing image signals from the respective solid-state photodetectors on each other to acquire a radiation image, as described in Patent Literature 1 below. In this apparatus, the photodetector elements are coupled to the X-ray entrance surface and to the back surface behind it in the scintillator and the visible light is detected by each of the entrance-surface-side photodetector element and the back-surface-side photodetector element, thereby increasing efficiency of detection of the visible light.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-open No. H07-27866

SUMMARY OF INVENTION Technical Problem

The apparatus for detecting the scintillation light on the both surfaces of the scintillator as described above can acquire radiation images in different energy bands on the entrance surface side and on the back surface side behind it, so as to enable acquisition of so-called dual-energy images

In the foregoing conventional apparatus, however, the radiation transmitted by the object passes through the entrance-surface-side photodetector element to reach the scintillator, and for this reason, radiation in a relatively low energy band is absorbed by the entrance-surface-side photodetector element. For example, when the object is formed of a lightweight atom, the radiation transmitted by the object can be absorbed by the entrance-surface-side photodetector element. As described above, the conventional apparatus has the problem that the radiation transmitted by the object is affected by the entrance-surface-side photodetector element.

It is therefore an object of the present invention to provide a radiation image acquisition device capable of acquiring radiation images in different energy bands while reducing the influence on the radiation transmitted by the object.

Solution to Problem

A radiation image acquisition device according to one aspect of the present invention includes: a radiation source which emits radiation; a wavelength conversion member of a flat plate shape which generates scintillation light according to incidence of the radiation emitted from the radiation source and transmitted by an object; first imaging means which condenses and images the scintillation light emitted from an entrance surface for the radiation in the wavelength conversion member; and second imaging means which condenses and images the scintillation light emitted from a surface opposite to the entrance surface in the wavelength conversion member, wherein one of the first imaging means and the second imaging means condenses the scintillation light emitted from the entrance surface or the opposite surface in a direction of a normal thereto, and wherein the other of the first imaging means and the second imaging means condenses the scintillation light emitted from the entrance surface or the opposite surface in a direction inclined with respect to a direction of a normal thereto.

In the radiation image acquisition device according to the one aspect of the present invention, the first imaging means and the second imaging means condense and image the respective scintillation light beams emitted from the entrance surface for the radiation and from the opposite surface behind it in the wavelength conversion member. This realizes dual-energy imaging to acquire radiation images in different energy bands. In this connection, the first imaging means is arranged at a position apart from the wavelength conversion member, in order to condense the scintillation light emitted from the entrance surface. Therefore, the radiation image acquisition device can have the configuration wherein no imaging means is interposed between the object and the wavelength conversion member, thereby avoiding an incident such that the imaging means affects the radiation transmitted by the object. Accordingly, it is feasible to reduce the influence on the radiation transmitted by the object. Furthermore, since one of the first imaging means and the second imaging means condenses the scintillation light emitted from the entrance surface or from the opposite surface behind it in the direction of the normal thereto, it can acquire a radiation image with no perspective. Therefore, a perspective of the radiation image acquired by the other imaging means can be properly corrected using the radiation image with no perspective acquired by the one imaging means, as a reference image.

The radiation image acquisition device may be configured in a mode such that each of the first imaging means and the second imaging means has: a condensing lens unit for condensing the scintillation light emitted from the wavelength conversion member; and an imaging unit for imaging the scintillation light thus condensed. In this case, the scintillation light is condensed with focus on each of the entrance surface and the opposite surface of the wavelength conversion member, which enables acquisition of bright radiation images with good energy separation.

The radiation image acquisition device may be configured in a mode such that the first imaging means condenses the scintillation light emitted in the direction of the normal to the entrance surface and that the second imaging means condenses the scintillation light emitted in the direction inclined with respect to the direction of the normal to the opposite surface. In this case, since the radiation image acquired by the first imaging means is an image of the scintillation light resulting from conversion near the entrance surface of the wavelength conversion member, it is less affected by a blur made inside the wavelength conversion member and thus becomes a clear image without a significant blur. Therefore, the radiation image with no perspective nor significant blur can be used as the reference image, whereby the better reference image can be used to correct for the perspective of the radiation image acquired by the second imaging means.

The radiation image acquisition device may be configured in a mode such that the radiation source is arranged on the normal to the entrance surface and that the first imaging means is arranged at a position off the normal to the entrance surface so as to condense the scintillation light via a reflecting mirror arranged between the wavelength conversion member and the radiation source. In this case, the radiation image with no perspective nor significant blur can be used as the reference image, as described above. In addition, since the radiation source is arranged on the normal to the entrance surface, no perspective is made in a projection image on the wavelength conversion member, which eliminates a need for an operation to correct for a perspective of the projection image. Furthermore, the first imaging means can be prevented from being exposed to the radiation, which can suppress generation of noise inside the first imaging means.

The radiation image acquisition device may be configured in a mode such that the second imaging means is arranged at a position off the normal to the opposite surface so as to condense the scintillation light emitted in the direction of the normal to the opposite surface, via a reflecting mirror arranged on the normal to the opposite surface. In this case, the second imaging means can be prevented from being exposed to the radiation, which can suppress generation of noise inside the second imaging means. Therefore, when the radiation image acquired by the second imaging means is used as the reference image, the good reference image is also available. Furthermore, this configuration permits adjustment of optical path lengths from the wavelength conversion member to the first and second imaging means, which facilitates position alignment of the first and second imaging means. As a consequence of this, it becomes easier to match imaging conditions of the first and second imaging means (e.g., simultaneity of imaging times and identity of imaging positions).

The radiation image acquisition device may be configured in a mode such that a tapered fiber is arranged between the opposite surface of the wavelength conversion member and the second imaging means so as to face the opposite surface. In this case, the tapered fiber can condense the scintillation light on the opposite surface side at a high light condensing efficiency. Furthermore, the tapered fiber blocks the radiation whereby the second imaging means can be prevented from being exposed to the radiation. Therefore, when the radiation image acquired by the second imaging means is used as the reference image, the good reference image is also available.

The radiation image acquisition device may be configured in a mode such that the device further includes: correction means for correcting an image taken by the other imaging means, using an image taken by the one imaging means, as a reference image.

The radiation image acquisition device may be configured in a mode such that the object is a semiconductor device and that the radiation image acquisition device is applied to a semiconductor failure inspection device an inspection target of which is the semiconductor device. In this case, since the radiation transmitted by the semiconductor device as the inspection target is not cut by the imaging unit (imaging device for acquisition of image), the inspection device can detect a failure or the like of the semiconductor device with high accuracy.

Advantageous Effect of Invention

The one aspect of the present invention enables the acquisition of radiation images in different energy bands and the reduction of the influence on the radiation transmitted by the object.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of the radiation image acquisition device according to the first embodiment of the present invention.

FIG. 2 is an explanatory drawing for explaining a projection image in the radiation image acquisition device shown in FIG. 1.

FIG. 3 is an explanatory drawing for explaining a correction for a perspective of an image in the radiation image acquisition device shown in FIG. 1.

FIG. 4 is a front view of the radiation image acquisition device according to the second embodiment of the present invention.

FIG. 5 is an explanatory drawing for explaining a correction for a perspective of an image in the radiation image acquisition device shown in FIG. 4.

FIG. 6 is a front view of the radiation image acquisition device according to the third embodiment of the present invention.

FIG. 7 is an explanatory drawing for explaining a perspective of a projection image in the radiation image acquisition device shown in FIG. 6.

FIG. 8 is a front view of the radiation image acquisition device according to the fourth embodiment of the present invention.

FIG. 9 is a front view of the radiation image acquisition device according to the fifth embodiment of the present invention.

FIG. 10 is a front view of the radiation image acquisition device which is a modification example of the present invention.

FIGS. 11(a) and (b) is front views of the radiation image acquisition devices which are modification examples of the present invention.

FIG. 12(a) to (c) is front views of the radiation image acquisition devices which are modification examples of the present invention.

FIG. 13 is an explanatory drawing about a modification example of the correction for a perspective of an image.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below in detail with reference to the drawings. Identical or equivalent portions will be denoted by the same reference signs in the description of the drawings, without redundant description. It is noted that each drawing is prepared by way of illustration only and is depicted so as to emphasize each part as object of description in particular. For this reason, the dimensional ratios of respective members in the drawings are not always coincident with actual ones.

As shown in FIG. 1, the radiation image acquisition device 1 is a device for acquiring a radiation image of an object A, e.g., an electronic component such as a semiconductor device, or a foodstuff. The radiation image acquisition device 1 is provided with a radiation source 2 which emits radiation such as white X-rays toward the object A, a wavelength conversion plate 6 which generates scintillation light according to incidence of the radiation transmitted by the object A after emitted from the radiation source 2, a front observation photodetector 3 which condenses and images the scintillation light emitted from an entrance surface 6 a for the radiation in the wavelength conversion plate 6, and a back observation photodetector 4 which condenses and images the scintillation light emitted from a back surface 6 b being a surface opposite to the entrance surface 6 a. These radiation source 2, wavelength conversion plate 6, front observation photodetector 3, and back observation photodetector 4 are housed in a housing not shown and fixed in the housing.

The wavelength conversion plate 6 is a wavelength conversion member of a flat plate shape, e.g., a scintillator of any one of Gd₂O₂S:Tb, Gd₂O₂S:Pr, CsI:Tl, CdWO₄, CaWO₄, Gd₂SiO₅:Ce, Lu_(0.4)Gd_(1.6)SiO₅, Bi₄Ge₃O₁₂, Lu₂SiO₅:Ce, Y₂SiO₅, YAlO₃:Ce, Y₂O₂S:Tb, YTaO₄:Tm, and so on. The thickness of the wavelength conversion plate 6 is set to an appropriate value depending upon a radiation energy band detected, in the range of several μm to several mm.

The front observation photodetector 3 (which will be referred to hereinafter as “front detector 3”) is an imaging means of an indirect conversion method that photographs a projection image (radiation transmission image) of the object A projected on the wavelength conversion plate 6, from the entrance surface 6 a side of the wavelength conversion plate 6. The front detector 3 is a detector of a lens coupling type having a condensing lens unit 3 a for condensing the scintillation light emitted from the entrance surface 6 a of the wavelength conversion plate 6, and an imaging unit 3 b for imaging the scintillation light condensed by the condensing lens unit 3 a. The condensing lens unit 3 a condenses the scintillation light in a front detector field 13. The imaging unit 3 b to be used herein is, for example, a CMOS sensor, a CCD sensor, or the like. When the front detector 3 corresponds to the below-described one imaging means, a light receiving surface of the imaging unit 3 b can be arranged approximately parallel to the entrance surface 6 a.

The back observation photodetector 4 (which will be referred to hereinafter as “back detector 4”) is an imaging means of the indirect conversion method that photographs a projection image (radiation transmission image) of the object A projected on the wavelength conversion plate 6, from the back surface 6 b side of the wavelength conversion plate 6. The back detector 4 is a detector of the lens coupling type having a condensing lens unit 4 a for condensing the scintillation light emitted from the back surface 6 b of the wavelength conversion plate 6, and an imaging unit 4 b for imaging the scintillation light condensed by the condensing lens unit 4 a, and thus it has the same configuration as the aforementioned front detector 3. The condensing lens unit 4 a condenses the scintillation light in a back detector field 14. The imaging unit 4 b to be used herein is, for example, a CMOS sensor, a CCD sensor, or the like. When the back detector 4 corresponds to the below-described one imaging means, a light receiving surface of the imaging unit 4 b can be arranged approximately parallel to the back surface 6 b.

Furthermore, the radiation image acquisition device 1 is provided with a timing control unit 7 for controlling imaging timing at the front detector 3 and at the back detector 4, an image processing device 8 for receiving input image signals from the front detector 3 and from the back detector 4 and executing a predetermined processing procedure such as image processing based on each of the input image signals, and a display device 9 for receiving an input image signal from the image processing device 8 and displaying a radiation image. The timing control unit 7 and the image processing device 8 are composed of a computer having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), input/output interfaces, and so on. The display device 9 to be used herein is a well-known display. The timing control unit 7 and the image processing device 8 may be configured as a program executed by a single computer or as respective units provided individually.

The below will describe the positional relationship among the aforementioned radiation source 2, wavelength conversion plate 6, front detector 3, and back detector 4. As shown in FIG. 1, the radiation source 2 is arranged so that an optical axis X of the radiation coincides with a normal B to the entrance surface 6 a of the wavelength conversion plate 6. Namely, the radiation source 2 faces the object A and the entrance surface 6 a and is arranged on the normal B to the entrance surface 6 a. The optical axis X of the radiation herein is a straight line connecting a radiation emission point of the radiation source 2 and an arbitrary point γ on the entrance surface 6 a of the wavelength conversion plate 6. In the present embodiment, the arbitrary point γ is set to be a central point of the entrance surface 6 a and in this case, the radiation is radiated with little relative unevenness. The normal B here is a straight line extending normally to the entrance surface 6 a from an arbitrary point α on the entrance surface 6 a. In the present embodiment, the arbitrary point α is set to be the central point of the entrance surface 6 a and thus the optical axis X of the radiation and the normal B coincide with each other. It is a matter of course that the arbitrary point γ and the arbitrary point α do not have to be coincident with the central point of the entrance surface 6 a.

The front detector 3 is arranged so that an optical axis F of the incorporated condensing lens unit 3 a makes a predetermined angle θ₁ with respect to the normal B to the entrance surface 6 a, so as to be able to image the scintillation light emitted from the entrance surface 6 a of the wavelength conversion plate 6. Namely, the front detector 3 faces the entrance surface 6 a and is arranged at a position off the normal B to the entrance surface 6 a. This condensing lens unit 3 a focuses on the entrance surface 6 a and condenses the scintillation light emitted in a direction at the angle θ₁ to the normal B from the entrance surface 6 a, toward the imaging unit 3 b. The condensing lens unit 3 a to be used herein can be a shift lens or a tilt lens. This front detector 3 corresponds to the other imaging means for condensing the scintillation light emitted in the direction inclined with respect to the direction of the normal B from the entrance surface 6 a.

As described above, the front detector 3 is arranged off the optical axis X of the radiation source 2. Namely, the front detector 3 is arranged so as to be located apart from an emission region of the radiation from the radiation source 2 (which is a region where a radiation beam 12 exists). This arrangement prevents the front detector 3 from being exposed to the radiation from the radiation source 2 and prevents a direct conversion signal of radiation from being produced inside the front detector 3 to generate noise.

The back detector 4 is arranged so that an optical axis G of the incorporated condensing lens unit 4 a is perpendicular to the back surface 6 b, so as to be able to image the scintillation light emitted from the back surface 6 b of the wavelength conversion plate 6. In this configuration, the optical axis G of the condensing lens unit 4 a is coincident with a normal C to the back surface 6 b. Namely, the back detector 4 faces the back surface 6 b and is arranged on the normal C to the back surface 6 b. Therefore, the back detector 4 can image the scintillation light emitted in the direction of the normal C to the back surface 6 b and thus readily acquire an image without a significant perspective. The normal C here is a straight line extending normally to the back surface 6 b from an arbitrary point β on the back surface 6 b. Particularly, in the present embodiment, the arbitrary point β is set at a central point of the back surface 6 b, the arbitrary point α on the entrance surface 6 a and the arbitrary point β on the back surface 6 b are located on the same straight line, and this straight line is coincident with the normal B and the normal C. The condensing lens unit 4 a focuses on the back surface 6 b and condenses the scintillation light emitted in the direction of the normal C from the back surface 6 b, toward the imaging unit 4 b. This back detector 4 corresponds to the one imaging means for condensing the scintillation light emitted in the direction of the normal C from the back surface 6 b.

In the radiation image acquisition device 1, an optical path length from the entrance surface 6 a of the wavelength conversion plate 6 to the front detector 3 is equal to an optical path length from the back surface 6 b of the wavelength conversion plate 6 to the back detector 4. The optical path length from the entrance surface 6 a of the wavelength conversion plate 6 to the front detector 3 may be different from the optical path length from the back surface 6 b of the wavelength conversion plate 6 to the back detector 4, but in this case, the sizes of the images need to be matched by image processing or the like.

The following will describe the operation of the radiation image acquisition device 1 having the above-described configuration. First, the timing control unit 7 performs control to make the front detector 3 and the back detector 4 simultaneously carry out their respective imaging operations. The imaging of radiation transmission images of the object A in different energy bands can be implemented based on the imaging timing control by the timing control unit 7. In more detail, the front detector 3 acquires the radiation transmission image in a relatively low energy band and the back detector 4 the radiation transmission image in a relatively high energy band. This operation realizes dual-energy imaging. It is noted that the radiation image acquisition device 1 is configured to allow control to make the imaging times of the front detector 3 and the back detector 4 different from each other. The device may also be configured to control the front detector 3 and the back detector 4 to different exposure times and/or different numbers of photos taken thereby.

The functions of the front detector 3 and the back detector 4 will be specifically described in more detail. The front detector 3 detects fluorescence (scintillation light) resulting from conversion on the side relatively near the entrance surface 6 a. The detection of the fluorescence resulting from the conversion on the entrance surface 6 a side is characterized by little blurring of fluorescence and high luminance of fluorescence. This is because the front observation can be less affected by diffusion and self-absorption inside the wavelength conversion plate 6. On the other hand, the back detector 4 detects fluorescence resulting from conversion on the side relatively near the back surface 6 b of the wavelength conversion plate 6. In this case as well, the observation can be less affected by diffusion and self-absorption inside the wavelength conversion plate 6.

Next, the front detector 3 and the back detector 4 output their respective image signals corresponding to the radiation images on both of the front and back surfaces, to the image processing device 8. When the image processing device 8 receives the respective input image signals from the front detector 3 and from the back detector 4, the image processing device 8 executes the predetermined processing such as an inter-image operation, e.g., a perspective correction, a differential operation, or an addition operation, based on the input image signals, and outputs an image signal after the image processing to the display device 9. When the display device 9 receives the input image signal after the image processing from the image processing device 8, the display device 9 displays a radiation image according to the input image signal after the image processing.

FIG. 2(a) is a perspective view showing the positional relationship among the radiation source 2, object A, and wavelength conversion plate 6 in the radiation image acquisition device 1, FIG. 2(b) a front view showing the positional relationship among the radiation source 2, object A, and wavelength conversion plate 6, and FIG. 2(c) a plan view showing a projection image D of the object A projected on the wavelength conversion plate 6. FIG. 2 shows a situation in which the object A is of a 3D shape, for easier understanding. When the radiation source 2 is arranged on the normal B to the entrance surface 6 a and the optical axis X of the radiation coincides with the normal B to the entrance surface 6 a as shown in FIG. 2(a), no perspective is made in the projection image D onto the entrance surface 6 a, as shown in FIG. 2(c).

FIG. 3(a) is a perspective view showing the positional relationship among the front detector 3, back detector 4, and wavelength conversion plate 6 in the radiation image acquisition device 1, FIG. 3(b) a drawing showing a front-side image Pa acquired by the front detector 3 and fed to the image processing device 8, and FIG. 3(c) a drawing showing a back-side image Pb acquired by the back detector 4 and fed to the image processing device 8.

When the front detector 3 is arranged at the position off the normal B to the entrance surface 6 a and the optical axis F makes the predetermined angle θ₁ with respect to the normal B to the entrance surface 6 a as shown in FIG. 3(a), a perspective is made in the front-side image Pa, as shown in FIG. 3(b). On the other hand, when the back detector 4 is arranged on the normal C to the back surface 6 b and the optical axis G is coincident with the normal C, no perspective is made in the back-side image Pb, as shown in FIG. 3(c).

The image processing device 8 recognizes a portion of the projection image D on the wavelength conversion plate 6 as a feature part d (a colored portion corresponding to a side face of the object A, in the example of FIG. 3). The perspective appears uniform in a front-side wavelength-conversion-plate image 20 a being a photographic image of the wavelength conversion plate 6, a front-side object image Ha being a photographic image of the object A, and a front-side feature-part image ha being a part of the front-side object image Ha and a photographic image of the feature part d, in the front-side image Pa.

Then the image processing device 8 functions as a correction means to correct for the perspective of the front-side image Pa using the back-side image Pb as a reference image. As a result, as shown in FIG. 3(d), the device acquires a corrected front-side image Pc without a perspective approximately matched with the back-side image Pb and generates an image signal corresponding to the front-side image Pc. Namely, this perspective correction process makes a front-side wavelength-conversion-plate image 20 c, a corrected front-side object image Hc, and a front-side feature-part image hc included in the corrected front-side image Pc approximately identical in position, size, and shape to a back-side wavelength-conversion-plate image 20 b, a back-side object image Hb, and a back-side feature-part image hb included in the back-side image Pb as the reference image.

In the radiation image acquisition device 1 of the present embodiment described above, the front detector 3 and the back detector 4 condense and image the respective scintillation light beams emitted from the entrance surface 6 a and the back surface 6 b of the wavelength conversion plate 6, thereby realizing the dual-energy imaging to acquire radiation images in different energy bands. In this configuration, the front detector 3 is arranged at the position apart from the wavelength conversion plate 6, without any detector interposed between the object A and the wavelength conversion plate 6. This configuration permits the device to avoid the incident that the imaging means affects the radiation transmitted by the object A. Therefore, the influence on the radiation transmitted by the object A is reduced and the radiation in a low energy band is suitably detected. In other words, no shadow of detector is cast on the radiation transmission images, so as to suppress generation of noise component and cause no attenuation of radiation due to the detector, thus suppressing reduction of signal components. As a result, it becomes feasible to make a difference between the low energy band and the high energy band in the dual-energy imaging larger and to exhibit a high energy resolution, allowing achievement of higher contrast. This advantage is prominently demonstrated, particularly, in the case where the object A is formed of silicon or an atom lighter in weight than silicon. Namely, even if the object A is formed of a lightweight atom, the radiation in the low energy band transmitted by the object A is converted into scintillation light, without being absorbed or attenuated, and this light is imaged by the front detector 3; therefore, the radiation image in the low energy band can be acquired with accuracy. Furthermore, the low-energy image and the high-energy image can be simultaneously acquired by a single imaging operation, so as to ensure simultaneity, reduce an exposure dose, and avoid pixel shifts (misregistration). The dual-energy imaging can be realized even by means of the single wavelength conversion plate 6. In addition, since the back detector 4 condenses the scintillation light emitted in the direction of the normal C to the back surface 6 b, it can acquire the back-side image Pb without a perspective, and the perspective of the front-side image Pa can be properly corrected using this back-side image Pb as a reference image.

When white X-rays are used as the radiation, the low-energy image and the high-energy image can also be simultaneously acquired by a single imaging operation of white X-rays, so as to ensure simultaneity, reduce an exposure dose, and avoid pixel shifts (misregistration).

As the condensing lens unit 3 a and the condensing lens unit 4 a condense the light with focus on each of the entrance surface 6 a and the back surface 6 b of the wavelength conversion plate 6, bright radiation images can be acquired with good energy separation.

FIG. 4 is a front view of the radiation image acquisition device according to the second embodiment. The radiation image acquisition device 1A shown in FIG. 4 is different from the radiation image acquisition device 1 of the first embodiment shown in FIG. 1 in that the front detector 3 is arranged at a position off the normal B to the entrance surface 6 a so as to condense the scintillation light via a reflecting mirror 15 arranged on the normal B (optical axis X) between the wavelength conversion plate 6 and the radiation source 2 and transmitting the radiation and in that the back detector 4 is arranged so that the optical axis G of the condensing lens unit 4 a makes a predetermined angle θ₂ with respect to the normal C to the back surface 6 b. FIG. 4 is depicted without illustration of the timing control unit 7, image processing device 8, and display device 9. FIGS. 6 and 8 to 12 are also depicted similarly without illustration of these components.

The configuration of the radiation image acquisition device 1A will be described more specifically. The reflecting mirror 15 is arranged so that its reflective surface 15 a makes a predetermined angle (e.g., 45°) with respect to the direction of the normal B so as to reflect the scintillation light emitted in the direction of the normal B from the entrance surface 6 a, into a predetermined direction relative to the normal B. The reflecting mirror 15 to be used herein is, for example, an optical mirror. The front detector 3 is arranged so that an angle between the optical axis F of the incorporated condensing lens unit 3 a and the reflective surface 15 a is equal to the angle between the normal B and the reflective surface 15 a. This condensing lens unit 3 a condenses the scintillation light emitted in the direction of the normal B from the entrance surface 6 a and reflected into the predetermined direction relative to the normal B by the reflecting mirror 15, toward the imaging unit 3 b. This front detector 3 corresponds to the one imaging means for condensing the scintillation light emitted in the direction of the normal B from the entrance surface 6 a.

The back detector 4 faces the back surface 6 b and is arranged at a position off the normal C to the back surface 6 b. This condensing lens unit 4 a condenses the scintillation light emitted from the back surface 6 b in a direction at the angle θ₂ to the normal C, toward the imaging unit 4 b. The condensing lens unit 4 a to be used herein can be a shift lens or a tilt lens. This back detector 4 corresponds to the other imaging means for condensing the scintillation light emitted from the back surface 6 b in the direction inclined with respect to the direction of the normal C.

As described above, the front detector 3 is arranged so as to be apart from the radiation emission region from the radiation source 2 (the region where the radiation beam 12 exists). This arrangement prevents the front detector 3 from being exposed to the radiation from the radiation source 2, and thus prevents a direct conversion signal of radiation from being produced inside the front detector 3 to generate noise. Furthermore, the optical path length from the entrance surface 6 a of the wavelength conversion plate 6 to the front detector 3 may be set equal to the optical path length from the back surface 6 b of the wavelength conversion plate 6 to the back detector 4.

In the radiation image acquisition device 1A, no perspective is made in the projection image D onto the entrance surface 6 a (cf. FIG. 2), either, as in the radiation image acquisition device 1.

FIG. 5(a) is a perspective view showing the positional relationship among the front detector 3, back detector 4, and wavelength conversion plate 6 in the radiation image acquisition device 1A, FIG. 5(b) a drawing showing the front-side image Pa acquired by the front detector 3 and fed to the image processing device 8, and FIG. 5(c) a drawing showing the back-side image Pb acquired by the back detector 4 and fed to the image processing device 8.

When the front detector 3 condenses the scintillation light emitted in the direction of the normal B from the entrance surface 6 a and reflected in the direction perpendicular to the normal B to the entrance surface 6 a, toward the imaging unit 3 b as shown in FIG. 5(a), no perspective is made in the front-side image Pa, as shown in FIG. 5(b). On the other hand, when the back detector 4 is arranged at the position off the normal C to the back surface 6 b with the optical axis G making the predetermined angle θ₂ relative to the normal C to the back surface 6 b as shown in FIG. 5(a), a perspective is made in the back-side image Pb, as shown in FIG. 5(c).

Then the image processing device 8 recognizes a part of the projection image D on the wavelength conversion plate 6 as a feature part d (a colored portion corresponding to a side face of the object A, in the example of FIG. 5). The perspective appears uniform in a back-side wavelength-conversion-plate image 20 b being a photographic image of the wavelength conversion plate 6, a back-side object image Hb being a photographic image of the object A, and a back-side feature-part image hb being a part of the back-side object image Hb and a photographic image of the feature part d, in the back-side image Pb.

Then the image processing device 8 functions as a correction means to correct for the perspective of the back-side image Pb using the front-side image Pa as a reference image. As a result, as shown in FIG. 5(d), the device acquires a corrected back-side image Pd without a perspective approximately matched with the front-side image Pa and generates an image signal corresponding to the back-side image Pd. Namely, this perspective correction process makes a back-side wavelength-conversion-plate image 20 d, a back-side object image Hd, and a back-side feature-part image hd included in the corrected back-side image Pd approximately identical in position, size, and shape to a front-side wavelength-conversion-plate image 20 a, a front-side object image Ha, and a front-side feature-part image ha included in the front-side image Pa as the reference image.

The radiation image acquisition device 1A achieves the same operational effect as the radiation image acquisition device 1 does. Since the front-side image Pa acquired by the front detector 3 is the image of the scintillation light resulting from the conversion near the entrance surface 6 a of the wavelength conversion plate 6, it is less affected by a blur made inside the wavelength conversion member 6 and thus becomes a clear image without a significant blur. Therefore, the clear front-side image Pa with no perspective nor significant blur can be used as the reference image, whereby the better reference image is available for the correction for the perspective of the back-side image Pb acquired by the back detector 4.

The perspective correction process by the image processing device 8 is to correct the back-side image Pb on the basis of the clear front-side image Pa without a significant blur as the reference image, whereby a clear tomographic image is also obtained as an image resulting from the inter-image operation between the front-side image Pa and the back-side image Pd.

In addition, since the radiation source 2 is arranged on the normal B to the entrance surface 6 a, no perspective is made in the projection image D onto the wavelength conversion plate 6, either, which eliminates a need for a correction for a perspective of the projection image D. Furthermore, the front detector 3 is prevented from being exposed to the radiation, which prevents generation of noise inside the front detector 3.

FIG. 6 is a front view of the radiation image acquisition device according to the third embodiment. The radiation image acquisition device 1B shown in FIG. 6 is different from the radiation image acquisition device 1A of the second embodiment shown in FIG. 4 in that the radiation source 2 is arranged so that the optical axis X of the radiation makes a predetermined angle θ with respect to the normal B to the entrance surface 6 a and in that the front detector 3 is arranged on the normal B to the entrance surface 6 a. More specifically, the front detector 3 is arranged so that the optical axis F of the condensing lens unit 3 a is perpendicular to the entrance surface 6 a. In this embodiment, the optical axis F of the condensing lens unit 3 a is coincident with the normal B to the entrance surface 6 a. Furthermore, the back detector 4 is arranged so that the optical axis G of the condensing lens unit 4 a and the optical axis X of the radiation source 2 are located on the same plane and on the same side with respect to the normals B, C. It is noted herein that the arbitrary point γ and the arbitrary point α do not have to be the central point of the entrance surface 6 a and do not have to be the same point, either.

As described above, the front detector 3 is arranged off the optical axis X of the radiation source 2. Namely, the front detector 3 is arranged apart from the radiation emission region from the radiation source 2 (the region where the radiation beam 12 exists). This arrangement prevents the front detector 3 from being exposed to the radiation from the radiation source 2 and thus prevents a direct conversion signal of radiation from being produced inside the front detector 3 to generate noise.

FIG. 7(a) is a perspective view showing the positional relationship among the radiation source 2, object A, and wavelength conversion plate 6 in the radiation image acquisition device 1B, FIG. 7(b) a front view showing the positional relationship among the radiation source 2, object A, and wavelength conversion plate 6, and FIG. 7(c) a plan view showing a projection image E of the object A projected on the wavelength conversion plate 6. FIG. 7 shows a situation in which the object A is of a 3D shape, for easier understanding. When the radiation source 2 is arranged at the position off the normal B to the entrance surface 6 a and the optical axis X of the radiation makes the predetermined angle θ with respect to the normal B to the entrance surface 6 a as shown in FIG. 7(a), a perspective is made in the projection image E onto the entrance surface 6 a, as shown in FIG. 7(c). This perspective of the projection image E is corrected according to needs by the image processing device 8. Although FIG. 7(a) shows that the main body of the radiation source 2 is parallel to the optical axis X, for convenience' sake of explanation, the orientation of arrangement of the radiation source 2 can be optionally set according to the layout of the device.

The radiation image acquisition device 1B achieves the same operational effect as the radiation image acquisition devices 1 and 1A do.

FIG. 8 is a front view of the radiation image acquisition device according to the third embodiment. The radiation image acquisition device 1C shown in FIG. 8 is different from the radiation image acquisition device 1 of the first embodiment shown in FIG. 1 in that the back detector 4 is arranged at a position off the normal C to the back surface 6 b so as to condense the scintillation light via a reflecting mirror 16 arranged on the normal C. More specifically, the reflecting mirror 16 is arranged so that its reflective surface 16 a makes a predetermined angle (e.g., 45°) with respect to the direction of the normal C and thus it reflects the scintillation light emitted in the direction of the normal C from the back surface 6 b, into a predetermined direction with respect to the normal C. The reflecting mirror 16 to be used herein is, for example, an optical mirror or a prism. The back detector 4 is arranged so that an angle between the optical axis G of the incorporated condensing lens unit 4 a and the reflective surface 16 a is equal to the angle between the normal C and the reflective surface 16 a. This condensing lens unit 4 a condenses the scintillation light emitted in the direction of the normal C from the back surface 6 b and reflected in the predetermined direction relative to the normal C by the reflecting mirror 16, toward the imaging unit 4 b.

As described above, the back detector 4 is arranged so as to be apart from the radiation emission region from the radiation source 2 (the region where the radiation beam 12 exists). This arrangement prevents the back detector 4 from being exposed to the radiation from the radiation source 2, and thus prevents a direct conversion signal of radiation from being produced inside the back detector 4 to generate noise. Furthermore, the optical path length from the entrance surface 6 a of the wavelength conversion plate 6 to the front detector 3 may be set equal to the optical path length from the back surface 6 b of the wavelength conversion plate 6 to the back detector 4.

The radiation image acquisition device 1C achieves the same operational effect as the radiation image acquisition devices 1, 1A, and 1B do. In addition, the back detector 4 is prevented from being exposed to the radiation, which prevents generation of noise inside the back detector 4. Furthermore, the optical path lengths from the wavelength conversion plate 6 to the front detector 3 and the back detector 4 are allowed to adjust, which facilitates position alignment of the first and second imaging means. As a consequence of this, it becomes easier to match the imaging conditions of the first and second imaging means (e.g., simultaneity of imaging times and identity of imaging positions).

FIG. 9 is a front view of the radiation image acquisition device according to the fifth embodiment. The radiation image acquisition device 1D shown in FIG. 9 is different from the radiation image acquisition device 1 of the first embodiment shown in FIG. 1 in that a tapered fiber 17 is arranged so as to face the back surface 6 b between the back surface 6 b and the back detector 4. More specifically, the tapered fiber 17 is arranged so that its axis is coincident with the normal C to the back surface 6 b, so as to guide the scintillation light emitted in the direction of the normal C from the back surface 6 b, to the condensing lens unit of the back detector 4. This tapered fiber 17 and the back detector 4 constitute a fiber coupling detector 18.

The radiation image acquisition device 1D achieves the same operational effect as the radiation image acquisition devices 1, and 1A to 1C do. The tapered fiber 17 condenses the scintillation light on the back surface 6 b side at a high light condensing efficiency. An ordinary fluorescent image tends to become dark on the back surface 6 b side of the wavelength conversion plate 6, but a loss in the optical system can be reduced by adopting the fiber coupling detector 18. Furthermore, the tapered fiber 17 blocks the radiation from the radiation source 2, so as to prevent exposure of the back detector 4 thereto.

The above described the embodiments of the present invention but the present invention is by no means intended to be limited to the above embodiments. For example, as shown in FIG. 10, the radiation image acquisition device 1E may be so configured that the radiation source 2 is arranged off the normal B to the entrance surface 6 a and that the reflecting mirror 15 is arranged on the entrance surface 6 a side. In this case, the back detector 4 is arranged so that the optical axis G of the condensing lens unit 4 a and the optical axis X of the radiation source 2 are located on the same plane and on the same side with respect to the normals B, C.

Furthermore, various modifications as shown in FIG. 11 may be adopted in the configuration wherein the radiation source 2 is arranged off the normal B to the entrance surface 6 a. Specifically, as shown in FIG. 11(a), the radiation image acquisition device 1F may be so configured that the front detector 3 is arranged on the normal B to the entrance surface 6 a and that the back detector 4 is arranged so that the optical axis G of the condensing lens unit 4 a makes the predetermined angle θ₂ with respect to the normal C to the back surface 6 b. In this modification, the back detector 4 is arranged so that the optical axis G of the condensing lens unit 4 a and the optical axis X of the radiation source 2 are located on the same plane and on the sides opposite to each other with respect to the normals B, C. Furthermore, as shown in FIG. 11(b), the radiation image acquisition device 1G may be so configured that the reflecting mirror 15 is arranged on the entrance surface 6 a side and that the back detector 4 is arranged so that the optical axis G of the condensing lens unit 4 a makes the predetermined angle θ₂ with respect to the normal C to the back surface 6 b. In this case as well, the back detector 4 is arranged in the same manner as in the radiation image acquisition device 1F. In these radiation image acquisition devices 1F and 1G, the front detector 3 corresponds to the one imaging means and the back detector 4 to the other imaging means.

Furthermore, various modifications as shown in FIG. 12 can also be adopted in the configuration wherein the radiation source 2 is arranged off the normal B to the entrance surface 6 a. Specifically, as shown in FIG. 12(a), the radiation image acquisition device 1H may be so configured that the front detector 3 is arranged so that the optical axis F of the condensing lens unit 3 a makes the predetermined angle θ₁ with respect to the normal B to the entrance surface 6 a, and that the back detector 4 is arranged on the normal C to the back surface 6 b. Moreover, as shown in FIG. 12(b), the radiation image acquisition device 1J may be so configured that the front detector 3 is arranged so that the optical axis F of the condensing lens unit 3 a makes the predetermined angle θ₁ with respect to the normal B to the entrance surface 6 a, and that the reflecting mirror 16 is arranged on the back surface 6 b side. Furthermore, as shown in FIG. 12(c), the radiation image acquisition device 1K may be so configured that the front detector 3 is arranged so that the optical axis F of the condensing lens unit 3 a makes the predetermined angle θ₁ with respect to the normal B to the entrance surface 6 a, and that the fiber coupling detector 18 is arranged on the back surface 6 b side. In these radiation image acquisition devices 1H, 1J, and 1K, the back detector 4 corresponds to the one imaging means and the front detector 3 corresponds to the other imaging means.

The above embodiments described the examples wherein the perspective correction by the image processing device 8 was to correct the image with a perspective using the image of the feature part d of the projection image D, but the perspective correction does not have to be limited to this technique. For example, the perspective correction may be made, as shown in FIG. 13, in such a manner that correction marks (signs) R are given at corners (two corners on a diagonal line on the wavelength conversion plate 6 in the example of FIG. 13) on the entrance surface 6 a and on the back surface 6 b of the wavelength conversion plate 6 and that the correction is made using front-side correction-mark images Sa and back-side correction-mark images Sb being images of the correction marks R. In the example shown in FIG. 13, the back-side image Pb is corrected for its perspective using the front-side image Pa as a reference image, thereby obtaining the corrected back-side image Pd. In this operation, the perspective correction is made so as to match the spaces and shapes between the front-side correction-mark images Sa in the front-side image Pa and corrected back-side correction-mark images Sd in the back-side image Pd. The correction marks on the wavelength conversion plate 6 may be a plurality of marks given at positions apart from each other, and a single mark will also suffice.

The above embodiments, in the cases using the reflecting mirror 15 or 16, described the examples wherein the reflecting mirror 15, 16 was arranged at the angle of 45° with respect to the normal B, C and wherein the optical axis of the condensing lens unit 3 a, 4 a was perpendicular to the normal B, C, but, without having to be limited to this arrangement, the angle of the reflecting mirror 15, 16 and the arrangement of the front detector 3 and the back detector 4 may be optionally modified according to the layout in the device.

The radiation source 2, front detector 3, and back detector 4 do not always have to be limited to the configuration wherein the optical axis X, the optical axis F, and the optical axis G are arranged on the same plane, but they may also be three-dimensionally arranged according to circumstances around the axis along the directions of the normals B, C.

The above embodiments described the mode in which when the front detector 3 condensed the scintillation light emitted in the direction inclined with respect to the direction of the normal B to the entrance surface 6 a, the front detector 3 was arranged so that the optical axis F of the condensing lens unit 3 a made the predetermined angle θ₁ with respect to the normal B to the entrance surface 6 a, but the present invention is not limited solely to this mode. For example, the front detector 3 may be arranged so that the optical axis F of the condensing lens unit 3 a is perpendicular to the entrance surface 6 a (i.e., parallel to the normal B) and the optical axis F is located outside the range of the entrance surface 6 a. In this case, the front detector 3 can also function as the other imaging means to condense and image the scintillation light emitted in a direction inclined with respect to the direction of the normal B from the entrance surface 6 a.

The above embodiments described the mode in which when the back detector 4 condensed the scintillation light emitted in the direction inclined with respect to the direction of the normal C to the back surface 6 b, the back detector 4 was arranged so that the optical axis G of the condensing lens unit 4 a made the predetermined angle θ₂ with respect to the normal C to the back surface 6 b, but the present invention is not limited solely to this mode. For example, the back detector 4 may be arranged so that the optical axis G of the condensing lens unit 4 a is perpendicular to the back surface 6 b (i.e., parallel to the normal C) and the optical axis G is located outside the range of the back surface 6 b. In this case, the back detector 4 can also function as the other imaging means to condense and image the scintillation light emitted in a direction inclined with respect to the direction of the normal C from the back surface 6 b.

The above embodiments used the lens coupling type detectors as detectors, but the condensing lens unit and the imaging unit may be provided as separate members.

An effective application is such that the object A is a semiconductor device and the radiation image acquisition device of the above embodiment is applied to a semiconductor failure inspection device an inspection target of which is the semiconductor device. In this case, the radiation transmitted by the semiconductor device as the inspection target is not cut by the imaging unit (imaging device for acquisition of image) and thus a failure or the like of the semiconductor device can be detected with accuracy.

INDUSTRIAL APPLICABILITY

The one aspect of the present invention enables the acquisition of radiation images in different energy bands and the reduction of the influence on the radiation transmitted by the object.

REFERENCE SIGNS LIST

-   -   1, 1A-1H, 1J, 1K radiation image acquisition devices; 2         radiation source; 3 front observation photodetector (first         imaging means); 3 a condensing lens unit; 3 b imaging unit; 4         back observation photodetector (second imaging means); 4 a         condensing lens unit; 4 b imaging unit; 6 wavelength conversion         plate (wavelength conversion member); 6 a entrance surface; 6 b         back surface (opposite surface); 8 image processing device         (correction means); 15 reflecting mirror; 16 reflecting mirror;         17 tapered fiber; A object; B normal to entrance surface; C         normal to back surface. 

The invention claimed is:
 1. An apparatus for capturing a radiation image, the apparatus comprising: a radiation source configured to emit radiation; a wavelength converter having an entrance plane, wherein the wavelength converter is configured to receive the radiation emitted from the radiation source through the entrance plane after the emitted radiation has been transmitted by an object, to convert the received radiation to scintillation light, and to output the scintillation light from the entrance plane; a first optical system including at least one lens, the first optical system being configured to focus on the entrance plane and to image the output scintillation light, thereby generating a first radiation image of the object; a first image sensor configured to capture the first radiation image; a second optical system including at least one lens, the second optical system being configured to focus on an opposite plane that is opposite to the entrance plane in the wavelength converter and to image scintillation light output from the opposite plane, thereby generating a second radiation image of the object; and a second image sensor configured to capture the second radiation image.
 2. The apparatus according to claim 1, wherein an optical axis of the first optical system is inclined with respect to a direction normal to the entrance plane.
 3. The apparatus according to claim 1, wherein an optical axis of the first optical system is perpendicular to the entrance plane.
 4. The apparatus according to claim 1, further comprising: a mirror configured to reflect the output scintillation light.
 5. The apparatus according to claim 1, wherein the wavelength converter comprises a scintillator.
 6. The apparatus according to claim 1, wherein an optical axis of the second optical system is inclined with respect to a direction normal to the opposite plane.
 7. The apparatus according to claim 1, wherein an optical axis of the second optical system is perpendicular to the opposite plane.
 8. The apparatus according to claim 1, further comprising: a mirror configured to reflect the scintillation light from the opposite plane.
 9. The apparatus according to claim 1, further comprising: an image processor configured to match a size of the first radiation image and a size of the second radiation image.
 10. A method for capturing a radiation image, the method comprising: emitting radiation from a radiation source; converting the radiation emitted from the radiation source to scintillation light after the emitted radiation has been transmitted by an object, wherein the converting is performed using a wavelength converter having an entrance plane; outputting the scintillation light from the entrance plane; imaging the output scintillation light, thereby generating a first radiation image of the object, using a first optical system that is focused on the entrance plane; capturing the first radiation image; outputting scintillation light from an opposite plane that is opposite to the entrance plane in the wavelength converter; imaging the output scintillation light from the opposite plane, thereby generating a second radiation image of the object, using a second optical system that is focused on the opposite plane; and capturing the second radiation image.
 11. The method according to claim 10, wherein the imaging is performed with an optical axis of the first optical system being inclined with respect to a direction normal to the entrance plane.
 12. The method according to claim 10, wherein the imaging is performed with an optical axis of the first optical system being perpendicular to the entrance plane.
 13. The method according to claim 10, wherein the converting is performed with the wavelength converter comprising a scintillator.
 14. The method according to claim 10, wherein the imaging is performed with an optical axis of the second optical system being inclined with respect to a direction normal to the opposite plane.
 15. The method according to claim 10, wherein the imaging is performed with an optical axis of the second optical system being perpendicular to the opposite plane.
 16. The method according to claim 10, further comprising: performing image processing, thereby matching a size of the first radiation image and a size of the second radiation image. 